The microwave dielectric properties of (1-x)La2/3TiO3-xLaAlO3 system in which LaAlO3 having $varepsilon$r$geq$90 and positive $ au$f was investigated. The crystal system of (1-x)La2/3TiO3-xLaAlO3 was pseudo-cubic in the range of 0.1$leq$x$leq$0.07. Its lattice constant increased with increasing x in spite that the amount of LaAlO3 containing of smaller Al(0.57 $AA$) ion than Ti(0.64 $AA$) increased. As the amount of LaAlO3 increased from x=0.1 to 0.9, the relative dielectric constant ($varepsilon$r) decreased from 50 to 23 and the temperature coefficient of resonant frequency($ au$f) decreased from +84 to -50. On the other hand, the value of Q.f0 reached a maximum (148,000 at 7 GHz) at x=0.7, where a rapid increase in the peak intensity of XRD occured, and further increased after prolonged sintering. The microwave dielectric properties of $varepsilon$r=37, Q.f0=47,000 (at 7 GHz), and $ au$f=-2 ppm/$^{circ}C$ were obtained near 0.6La2/3TiO3-0.4LaAlO3 (x=0.4) composition.